#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))

#define MOD 1000000007

#define N 201

double a[N][N],b[N],x[N]; 

void gj(int n){
  int i, j, k;
  double w, m, s;

  for(k = 0; k < n-1; k++){
    w = 1.0 / a[k][k];
    for(i = k + 1; i < n; i++){
      m = a[i][k] * w;
      for(j = k + 1; j < n; j++){
        a[i][j] -= m * a[k][j];
      }
      b[i] -= m * b[k];
    }
  }

  x[n-1] = b[n-1] / a[n-1][n-1];

  for(k = n-2; k >= 0; k--){
    s = 0.0;
    for(j = k + 1; j < n; j++){
      s += a[k][j] * x[j];
    }
    x[k] = (b[k] - s) / a[k][k];
  }
}

int main(){
  int k;
  cin >> k;
  clr(a,0);
  clr(b,0);
  rep(i,0,k){
    a[i][i] = 6;
    rep(j,1,7){
      if(i+j<=k){
        a[i][i+j]--;
      }
      else{
        a[i][0]--;
      }
    }
    b[i] = 6;
  }
  a[k][k] = 1;
  gj(k+1);
  cout << x[0] << endl;
  return 0;
}

/*
モンテカルロ封じで制約を20から200に変えました。
*/